Humans are estimated to be exposed to approximately 90,000 different compounds in the course of their daily lives. An unknown number of these chemicals are hormone active agents (HAA) that may also cause cancers, birth defects, or other diseases such as obesity, cardiovascular diseases, or neurological defects. Much of the work with HAA in the environment has been reductionist in nature, focusing on single receptors, or pathways. Thus linking exposure to HAA in the environment to specific human disease outcomes has been difficult. To understand the risk of disease to humans after exposure to HAAs detailed knowledge of molecular mechanisms is required. Recent advances in bioinformatics and computer-based data management and data mining have made holistic approach to biological science more feasible. To fully understand the interaction of HAA with complex biological systems requires an integration of experimental and computational research. The application of systems biology to the study of HAA interacting with human systems will add important insight into a broader understanding of the deleterious effects of HAAs on human health. Therefore, we will hold a symposium on the application of systems biology to the study of HAAs in the environment in conjunction with the Chemical Toxicology Division of the American Chemical Society at the 228th National Meeting in Philadelphia, PA, August 22-26, 2004. The goal is to make toxicologists aware of the power of systems biology and how systems biology approach can be applied to the important problem of understanding the action of HAA.